1. Field of the Invention
The present invention relates to a shape-variable optical element, an optical device provided therewith, and an image pickup apparatus.
2. Description of Related Art
In the conventional method, the optical element such as an optical lens is made of a rigid material such as glass and plastic. To constitute an optical system equipped with an autofocus function and optical zoom function, the optical lens must be moved mechanically in the optical direction.
An actuator such as a stepping motor, voice coil motor and piezo motor is generally employed for mechanical movement of the optical lens.
However, since such an optical system contains a movable section, manufacturing costs are high due to the complicated mechanism, and downsizing of the optical system is placed under restrictions.
To solve such problems, a variable focus lens based on the electro wetting effect has been proposed (e.g., Patent Document 1).
A proposal has been made of a reflection type shape-variable optical element wherein a piezoelectric material is used to change the curvature radius (e.g., Patent Document 2).
An optical system equipped with an autofocus function or optical zoom function can be produced by using the variable focus lens described in the Patent Document 1 or the shape-variable optical element described in the Patent Document 2, without having to use a mechanical movable section.
[Patent Document 1] International Publication Booklet No. 99/18456.
[Patent Document 2] Unexamined Japanese Patent Application Publication No. 2000-105306.
However, the variable focus lens described in the Patent Document 1 requires the shape on the interfaces of two different liquids to be stabilized, and this makes it difficult to increase the diameter. Further, such a variable focus lens that can meet the requirement is restricted only to the convex lens having a spherical form. It is not possible to meet the lenses of various shapes such as a concave lens, aspherical lens and Fresnel lens.
To make fine adjustment of the curvature radius in the shape-variable optical element described in the Patent Document 2, a piezoelectric material or electrode must be divided into a plurality of segments and voltage must be applied to each of them. This requires an unnecessarily complicated structure as an optical device.
The object of the present invention is to solve the aforementioned technical problems and to provide a shape-variable optical element characterized by a simple structure capable of increasing the diameter and meeting a great variety of shapes, an optical apparatus equipped with this shape-variable optical element, and an image pickup apparatus.